Process for treating impure lead



Patented Dec. 4, 192.8.

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GEORGE E. DALBEY, OF EAST BERLIN, AND THOMAS P. HANFORD, OF BERLIN, CON- NECTICUT, ASSIGNORS TO THE STANLEY CHEMICAL CONNECTICUT, A CORPORATION OF CONNECTICUT.

COMPANY, OF EAST BERLIN,

PROCESS FOR TREATING IMPURE LEAD.

No Drawing.

This invention relates to a process for treating impure lead. v

Impure lead usually contains one or more of the metals arsenic, tin and antimony. These metals also exist as alloying matter in lead alloys and it is to be understood that the term impure lead includes lead alloys.

It is an object ofthe invention to provide.

an effective and economical process for treating impure lead to remove arsenic, tin and antimony individually or collectively.

With this and other objects in view, the invention consists in the process which will first be described and then more particularly pointed out. p i

Considering first, for convenience of description, the removal of tin from an alloy of tin with lead, in carrying out the process of the invention, the alloy is melted and is treated in a molten condition in a receptacle suitablyelosed against an oxidizing atmosphere. Upon the molten alloy'is placeda suitable amount of an oxide of lead, e. g. litharge. The contents of the receptacle are stirred in any suitable manner and during thisstir'ring there is slowly added upon the surfaceof the lithargeand molten metal, a

water solution of a caustic alkali, e. g. sodium hydr0xide.- It will be understood that this 3 slow addition of the caustic alkali referredto may be intermittent, the eflect in View being I a. gradual addition rather than an abrupt ad dition o'fthe entire batch. As the water evaporates, the remaining sodium hydroxide becomes intimately mixed with and reacts with the litharge. The stirring operation keeps the particles of litharge and resulting sodium plumbate separated into a fine state of division. It also continuously brings the litharge, as it is being 'coated and ,treated with sodium hydroxide, into intimate. contact with the molten metal. From a chemical standpoint, it is probable that two reactions take place. First, the litharge is acted upon by the sodium hydroxide to form sodium plumba'te. Secondly, a certain amount of tin is oxided by the action of the litharge, the latter being reduced to metallic lead; There is also a reaction between the tin oxide thus produced and the sodium hydroxide to form sodium stannate. Also, areaction between the sodium plumbate and the tin in the molten al- 10y forms metallic lead and sodium stannate.

Application filed May 4, 1926. Serial no. 106,726.

During the periodof reaction, in carrying out the process to the best advantage, the ma. terials on the surface of the molten metal are maintained in a dry, powdery condition. In this way, avoiding the use of molten sodium hydroxide, the reaction is kept under proper control and extremely beneficial results are obtained.

If desired, after a certain reaction period, the dry, powdery material may be removed from the surface, a fresh batch of litharge provided, and a further reaction period carried out. The reaction may be-accelerated by causing a'portion of the molten allo to be raised, for example, by a pump, an al lowed to drop in globules onto and through the superimposed litharge. This gives an intimate contact of the molten metal with the 'litharge and the sodium plumbate, or sodium hydroxide, as the case may be. The process described may be amplified in many ways, e. g. by counter current operations in which the reagents and products of reaction may be removed from .one receptacle and placed on molten metal in another receptacle.

In any event, when the reaction period is continued for a suflicient time under proper conditions, substantially all the tin in the alloy is turned into sodiumstannate, leaving the molten metal substantially free from tin.

During the evaporation of the water of the sodium hydroxide solution, steam is formed in the closed receptacle and aids in preventing access of air to the materials undergoing reaction. The process described is applicable to the separation of arsenic and antimony from lead alloys. In the case of arsenic it is removed in the form of sodium arsenate and antimony is removed as sodium antimoniate.

In treating a lead alloy containing all these metals, i. e. arsenic, tin and antimony, they may all be removed by the process de- 1 scribed, in the order named. That is, there is sodium hydroxide substituted. Another periodof reaction is carried out, resulting in the removal of the tin. 'The powdery layer is again removed and another charge of reagents supplied. The final period of reaction removes the'antimony. Thus arsenic, tin and antimony are removed individually and separately from a lead alloy containing all these metals.

The above description sets forth the treatment of lead alloys. It will be understood that the treatment of impure lead is the same except that quantities may vary as in the case of impure lead the amounts of arsenic, tin and antimony present are usually smaller than in the case of alloys. In either case metallic lead is reclaimed. In the case of alloys, where the amounts of alloying metals are substantial, there is also obtained one or more alkali salts of such metals and these salts have commercial value.

What is claimed is:

1. The process of treating impure lead for the removal of arsenic, tin, antimony and the like, which comprises bringing the metal in a molten condition under the influence of litharge and at the same time making gradual additions of a water solution of a caustic alkali and maintaining the whole at a temerature which will always allow the reactmg materials on the surface of the molten metal to remain in a powdery or granular condition 2. The process of treating impure lead for the removal of arsenic, tin, antimony and the like, which comprises bringing the metal in a molten condition under the influence of an oxide of lead and at the same time making gradual additions of a water solution of a caustic alkali and maintaining the whole at a temperature which will alwaysallow the reacting materials on the surface of the moltenmetal to remain. in a powdery or granular condition. Y

3. The process of treating impure lead for the removal of arsenic, tin, antimony and the like, which comprises bringing the metal in a molten condition under the influence of litharge and at the same time making gradual additions of a Water solution of a caustic alkali and maintaining the whole at a temperature which will always allow the reacting materials on the surface of the molten metal to remain in, a powdery or-granular condition, and protecting the whole from an oxidizing atmosphere.

4. The process of treating impure lead for the removal of arsenic. tin, antimony and the like, which comprises bringing the metal in a molten condition under the influence of an oxide of lead and at the same time making gradual additions of a water solution of a caustic alkali and maintaining the Whole at a temperature which will always allow the reacting materials on the surface of the molten metal to remain in a powdery or granular condition, and protecting the whole from an oxidizing atmosphere.

In testimony whereof, we have hereunto set our hands.

GEORGE E. DALBEY. THOMAS P. HANFORD. 

